Measuring the freeness of pulp



p 1931- F. L. SIMONS ET AL 1,822,604

MEASURING THE FREENESS OF PULP Filed Aug. 22, 1929 2 Sheets-Sheet l p1931- F. SIMONS ET AL 1,822,604

MEASURING THE FREENESS OF PULP,

Filed Aug. 22, 192@ 2 Sheets-Sheet 2 INVENTORS Patented Sept. 8, 1931UNITED STATES PATENT OFFICE FRANCIS L. SIMONS, OF KENNEBUNK, MAINE,HERVEY J. SKINNER, OF WAKEFIELD, AND RAYMOND M. FUOSS, 0F CAMBRIDGE,MASSACHUSETTS, ASSIGNORS T0 SKINNER & SHERMAN INC., 01 BOSTON,MASSACHUSETTS, A CORPORATION OF MASSACHU- SETTS MEASURING THE FREENESS0F PULP Application filed August 22, 1929. Serial No. 387,778.

The present invention relates to measuring the freeness of pulp, andmore particularly to measuring the freeness of paper pulp, although theinvention may be applied to measuring the freeness of other fibrouspulps, such as those used in making pulp-board,

' fiber-board and the like.

The freeness of the pulp is usually measured by the rate at which waterwill drain from the pulp. A pulp is said to be free or slow, dependingupon whether the water drains from it freely or slowly. The beating ofthe pulp in the beater of the paper-making machinery tends tomechanically hydrate the cellulose fibers, giving different degrees ofhydration depending upon the length of time that the pul is beaten. Afree pulp is one in which the her is but little if any hydrated and inwhich the water can drain rapidly. This type of pulp gives a paper likeblotting paper. A slow pulp from which the water drains very slowly is ahighly hydrated pulp and in the extreme case gives a paper like glassinepaper.

We have found that the freeness' of the pulp may be measured by placingsuitably prepared samples of the pulp between the plates of thecondenser and measuring the dielectric capacity of the pulp sample. Aslow pulp has a greater dielectric capacity than a free pulp. Indeterming the dielectric capacity of the pulp formeasuring its freeness.recourse is preferably had to the application of high frequency currentstothe measuring condenser. These high frequency currents can be readilyproduced by an oscillator of the thermionic tube type which willgenerate currents of a million or more cycles per second. A secondarycircuit containing the condenser is loosely coupled with the oscillatorcircuit and tuned to it. When the capacity of the condenser is changed,the circuit will be thrown out of tune, the degree to which it is thrownout of tune being indicated by a change in the current of the secondarycircuit which can be read by a suitable instrument.

For'determining the freeness of the pulp, a sample of the thin pulp orwater suspension of fiber is taken from the beater of the papermakingmachine and with or without diluting is placed in a measuring vessel,and then the water drained out, leaving a pat of moist pulp. Thisstandard pat of moist pulp may then be placed between the plates of acondenser spaced apart a predetermined distance, and the dielectriccapacity of the pulp measured. A pat of free pulp will have the moisturedrained out of it fairly completely, whereas a pat of slow pulp willretain a considerable proportion of the moisture. The variations in thefreeness of the pulp may be measured by the change in the dielectriccapacity of the condenser caused by the different pulp samples. a

The freeness of the pulp may also be measured continuously, and thedegree of beating controlled in accordance therewith. This may be doneby draining a small stream of the pulp from the beater onto acontinuously moving screen through which the water may be drained toproduce a moving sheet of pulp. The dielectric capacity of the movingsheet of pulp may be continuously determined by passing it between theplates of the condenser and the changes in the freeness of the pulp canbe continuously determined.

In the drawings, which illustrate the preferred embodiment of ourinvention:

Figure 1 is a diagrammatic View showing a simplified form of oscillatingcircuit and tuned-in secondary circuit containing the condenser used formeasuring the freeness of the pulp;

Figure 2 is a modification showing a more complicated but more sensitiveand refined circuit; 1

Figures 3 and 4 are lan and vertical sectional views, respective y,through the vessel used for receiving a sample of the pulp suspensionfor measuring its freeness;

Figure 5 is a vertical section showmg the drained pat of pulp betweenthe plates of a measuring condenser;

Figure 6 is a diagrammatic elevation of a I device for continuouslymeasuring the freeness of pulp; and

Figure 7 is a fragmentarv view showing a modification ot the condenserused in the device of Figure 6.

Referring first to the simplified diag'am of Figure 1:

Reference numeral 2 indicates the usual thermionic vacuum tubecontaining the filament 3, grid 4 and pl ate 5. The filament 3 is heatedby the so-called A battery 6. A local or grid circuit 7 contains thecoil 8 and the adjustable or tuning condenser 9. The plate circuitcontains the coil 10. inductively mounted with respect to the coil 8.the plate or 13" batterv 11 and the coil 12 of the transformer 13. Theoscillating circuit thus described is a usual tvpe ot teed-backoscillating circuit. Oscillations are set up and amplified. producinghigh frequency oscillations through the plate circuit and coil 12. Thesecondary circuit 14 contains acoil 15. loosely coupled with the coil 12of the transformer 1?). It also contains an adinstablc tuning condenser16. Tu parallel with this condenser is the condenser 17. between theplates of which is placed the pulp for dielectric capacity measurements.The circuit 14 contains a suitable ciurent-measuring device 18.

RV suitably adjusting the tuning condenser 16. the secondary circuit 14may be tuned to the oscillator circuit when the condenser 17 has betweenits plates a pat or sheet of pulp of a predetermined treeness. A-variation from such predetermined condition will result in a variationin the capacity of the condenser 17. which will be indicated bv adecrease in the current as measured by the ammeter 18.

In Figure 2 are illustrated circuits giving greater sensitivity ofresponse. In Figure 2, reference numeral 20 indicates a thermionicvacuum tube having filament 21. grid 22 and plate 23. The filament issupplied bv the usual A battery 24. The local or grid circuit containsan inductance coil 25 and an adjustable tuning condenser 26. The platecircuit has the usual B battery 27 and coil 28 inductively coupled withthe coil 25. The plate circuit contains the choke coil 29 in series withthe battery 27. It also contains the condenser 30 and variableresistance 31 in series with the coil 28. A branch circuit connectedwith the plate contains the condenser 32 and a variable resistance 33,and the coil 34 of the transformer 35. The circuit above described willoperate as an oscillating circuit,

setting up a continuous train of oscillations through the coil 34.

A secondary circuit, indicated generally by the reference numeral 36,contains a coil 37, loosely coupled with the coil 34, and serving as aninput to the secondary circuit. The secondary circuit contains the usualthermionic vacuum tube 38, having the usual filament 39, grid 40, andplate 41. The grid circuit -12 contains the coupling coil 37, thecondenser 43, the tuning condenser 44 and bias battery 45. A branchcircuit 46 leads to a double-throw, double-pole switch 4:7, which may bethrown to the right to connect with a variable condenser 48. or to theleft to con nect with a condenser 49, which corresponds to the condenser17 of Figure 1; that is to say. it is the condenser between the platesof which is run or placed the pulp to be measured for its dielectriccapacity.

\Vith a standard pat or sheet of pulp hav' ing a predetermined freenessbetween the plates of the condenser 49, the grid circuit 42 may be tunedby means of the condenser H into resonance. A change in the dielectriccapacity of the condenser 49, which would result from a change in thefreeness of such standard pat or sheet, will result in a throwing of thecircuit more or less out of tune depending upon the magnitude of thevariation in dielectric capacity, thus diminishing the current fed inthe grid circuit 42. The adjustable condenser 48 may be adj ustcd to beof equal capacity to the condenser 19 when a standard pat or sheet ofpulp of a predetermined freeness is between the plates of the condenser49. lVith the condenser 48 thus adjusted, it may be used as a. check forthe resonance setting of the circuits in use.

The variations in the oscillating current in the grid circuit- 42 areamplified and rectified by the thermionic tube 40, giving measurablevariations in the plate circuit of this tube. The plate circuit of thetube, indicated generally by reference numeral 50, contains the usual Abattery 51 for heating the lilament 39. It contains the condenser 52 connccted between the plate and the filament. It is provided with a chokecoil 53 and adjustable resistance 54 in series with the usual plate or Bbattery 55. The plate circuit contains an adjustable resistance 56 andan ammeter or galvanon'ieter 57 which, by means of a single-pole,double-throw switch 58, may be either short circuited or connected inparallel with the resistance 56. The adjustment of the resistance 56controls the magnitude of the deflection of the galvanometcr. Since theresistance of the galvanometer is usually large compared with that ofthe resistance 56, the galvanometer may be either shunted aroundresistance 56 or short circuited without much change in the resistanceof the plate circuit. An auxiliary circuit 59 is connected across the Abattery 51, and contains the variable resistance 60 and 61 and aresistance 62, along which a contact point 63 may be moved. The contactpoint 63 is connected through wire 64 and resistance 65 to one side ofthe resistance 56 and galvanometer 57.

The circuit 59 and slide resistance 62 act as a potentiometer by meansof which electromotive force from the battery 51 may be opposed to theelectromotive force of the plate current through the resistance 56 andgalvanometer 57. In practice, the adjustable contact 63 is adjusteduntil the galvanometer shows a zero deflection. Then, if change takesplace in the capacity of the condenser 49, due to a change in thedielectric capacity of the material being measured, the capacity of thegrid circuit is chan ed and with it the effect of the grid upon theplate circuit, producing a change in the plate circuit current which ismeasured by a deflection of the galvanometer. Since the opposing currentfrom the potentiometer 62 through the galvanometer remains constant thechange in plate current is shown by the galvanometer deflection whichmay be used as a measure of the change in the capacity of the condenser49. It will therefore be seen that an increase or decrease in thecapacity of the condenser 49, due to the change in the dielectriccapacity of the materialbetween these plates, will be indicated by adeflection in the predetermined direction on the galvanometer scale.This arrangement gives a readily controlled and very sensitivedeterinination of small changes in the dielectriccapacity of thematerial between the condenser plates.

It will be seen from the wiring diagram that the apparatus affords atleast four methods of following changes in the capacity of the condenser49.

1. With the position of the potentiometer point 63 fixed and thecapacities 44 and 48 fixed, changes in the capacity of the condenser 49may be followed by changes in the galvanometer readings.

2. With the capacities 44 and 48 fixed, the galvanometer 57 may be usedas a null instrument and changes in the capacity of the condenser 49followed by changes in the setting of the potentiometer contact point63.

3. With the position of the potentiometer contact point 63 fixed and thecapacity of the condenser 44 fixed, the galvanometer 57 may be used as anull instrument and changes in the capacity of the condenser 49 followedby changes in the capacity of the condenser 48. For this method a thirdcondenser should be used as a check or reference capacity so that it canbesubstituted in the circuit for the condensers 48 and 49.

4. With the position of the potentiometer contact point 63 fixed and thecapacity of the condenser 48 fixed, the galvanometer may be used as anull instrument and changes in the capacity of the condenser 49 followedby changes in the capacity of the condenser 44.

As will be understood from the above explanation, the condenser 48 is,in the methods 1, 2 and 4 above outlined, used as a check on thecondenser 49. When the condenser 49 is in the predetermined or standardcondition having a predetermined or standard capacity, due to apredetermined dielectric capacity of the material between these plates,the condenser 48 may be adjusted to the same capacity and may beoccasionally thrown into circuit to check the readings of thegalvanometer for such standard condition.

For the determination of the freeness of the pulp by intermittentlytaking samples thereof, the device shown in Figures 3, 4 and 5 is used.This device consists of a ring 80 having an opening closed by awatertight removable plug 81. This opening is covered by a fine wirescreen 82. An open-ended cylindrical vessel 83 is placed in the ring 80making watertight contact with it. Then a sample of the thin pulp orwater suspension of fiber, dipped from the beater or other container forthe pulp whose freeness is to be measured, is poured into the vessel 83,just filling it or filling it to a predetermined height, or said samplemay be diluted with water before pouring into vessel 83. This watersuspension is indicated by reference numeral 84. Then the plug 81 isremoved, allowing the free water to drain from the pulp. When the freewater has dripped away, cylinder 83 is removed, leaving a pat 85 of wetpulp in the ring 80 on the screen 82. The ring 80 with the pat of wetpulp is then transferred to the condenser indicated generally byreference numeral 86 and shown in Figure 5. This condenser may be eitherthe condenser 17, indicated in Figure 1, or the condenser 49, indicatedin Figure 2. It comprises upper and lower plates 87 and 88,respectively, which are arranged to be separated a predetermineddistance. The ring 80 with the pat 85 of wet pulp 011 it is placed onthe lower plate 88 and accurately positioned thereon by means of threeconically pointed pins 89, which fit into depressions in the top of theplate 88.

Since a slow pulp retains more water than a free pulp, the capacity ofthe condenser 86 will be "aricd in accordance with the amount of waterheld in the pulp, and this capacity, when suitably calibrated, will givea direct determination of the freeness of the sample of pulp.

In Figure 6 is illustrated an apparatus for continuously measuring thefrecncss of pulp. A pulp from the beater is delivered into a mixing box90, through an inlet 91 in a small substantially continuous stream, asby a chain-and-bucket conveyor or centrifugal pump. The pulp is dilutedcontinuously with sufficient water to give a good thin mixture. Theinlet for the water is indicated by reference numeral 92, through whicha constant but adjusted stream of water may be admitted. An agitator 93mixes the pulp and water and serves to maintain a uniform suspension ofpulp. This suspenslon is fed over the overflow 94 on a slowly movingmetal paper-making screen 95, forming a moving sheet 96 of pulp. Thefree water drains from the pulp through the screen. The length and speedof the screen and the rate of flow are adjusted so that a uniform sheetof pulp forms and completely drains of its free water by the time itreaches the far end of the device, where the pulp passes through acondenser 97. After passing through the condenser, the pulp may bedumped back into the beater. The condenser 97 has an upper plate 98,spaced a predetermined distance above the screen 95. The metal screen 95may serve as the other plate of the condenser 97. Suitable leads 99 and100 lead from the plates of the condenser 97 to the device, whereby theelectrostatic capacity of the condenser 97 may be determined. Thecondenser may be either the condenser 17 of the circuits shown in Figure1, or the condenser 49 of the circuit shown in Figure 2.

The condenser 97 of the device shown in Figure 6 may be otherwiseconstructed. For example, instead of utilizing the screen as the lowerplate of the condenser, a separate plate 101 may be placed below theupper run of the screen 95, as shown in Figure 7.

The device shown in Figure 6 provides for the continuous determinationof the freeness or slowness of the pulp. The measurements may be read onan indicating instrument or the measurements, as shown by the currentchanges, may be made through a suitable contact device to automaticallycontrol the beater, and thereby automatically maintain a predetermineddesired freeness of the pulp in the paper-making machine.

In our copending application Serial No. 387,772 filed of even dateherewith, we have described and claimed a method and apparatus broadlyfor measuring the relation between the fiber and water contents offibrous pulps, and specifically, the measurements of the consistency ofpulp. The present application is directed specifically to measuring therelation between the fiber and water contents of fibrous pulps todetermine the freeness of the pulp.

While we have specifically illustrated and described the preferredembodiments of our invention, it is to be understood that the inventionis not so limited, but may be otherwise embodied and practiced withinthe scope of the following claims.

lVe claim:

1. The method of measuring the freeness of pulp, which consists inmeasuring its dielectric capacity.

2. The method of measuring the freeness of pulp, which consists indraining the free water from the pulp and then determining thedielectric capacity of the drained pulp.

3. The method of measuring the freeness of pulp, which comprisesmeasuring out a predetermined amount of the suspension of pulp in water,draining the free pulp from the suspension, and determining thedielectric capacity of the drained pulp.

4:. The method of measuring the freeness of pulp, which comprisesdraining the free water from the pulp, placing the drained pulp betweenthe plates of a condenser, and determining its capacity.

5. A device for measuring the freeness of pulp, which comprises a vesseladapted to be filled with a predetermined quantity of the watersuspension of the pulp fiber from which the free water may be drainedaway leaving a moist pat of pulp, a condenser, means for positioning themoist pat between the plates of the condenser and means for measuringthe capacity of the condenser.

6. A device for measuring the freeness of pulp, which comprises meansadapted to be supplied with a predetermined quantity of the watersuspension of the pulp fiber from which the free water may be drainedaway leaving a moist layer of pulp, a condenser, means for positioningthe moist layer of pulp between the plates of the condenser, and meansfor measuring the capacity of the condenser. 1

'7. A device for measuring the freeness of pulp, which comprises meansprovided with a draining screen and adapted to be supplied with apredetermined quantity of the water suspension of the pulp fiber fromwhich the water may be drained away through the screen leaving thereon amoist layer of the drained pulp, a condenser, means for posi tioning themoist layer of pulp between the plates of the condenser, and means formeasuring the capacity of the condenser.

8. A device for continuously measuring the freeness of pulp, comprisinga condenser, means for forming a continuous sheet of pulp, draining thefree water therefrom and passing the sheet from which the free water hasbeen drained but otherwise in an undried condition between the plates ofthe condenser, and means for detecting variations in the capacity of thecondenser due to variations in the freeness of the pulp.

9. A device for continuously measuring the freeness of pulp, comprisinga condenser, means for forming a continuous sheet of pulp, draining thefree water therefrom and passing the sheet from which the free water hasbeen drained but otherwise in an undried condition between the plates ofthe condenser, said means including a continuously moving screen andmechanism for delivering continuously to the screen a predeterminedquantity of water suspension of the pulp fiber, and means for detectingvariations in the capacity of the condenser due to variations in thefreeness of the pulp.

In testimony whereof we have hereunto set our hands.

FRANCIS L. SIMONS. HERVEY J. SKINNER. RAYMOND M. FUOSS.

